Linear motion guide units have been extensively used in recent years with installed in the relatively sliding parts in machinery including machine tools, semiconductor fabricating instruments, measurement equipment, assembling machines, and so on. The linear motion guide units diverse in their sizes and types have been developed into commercial products for a variety of needs or applications. Among the linear motion guide units of the sort balls are selected as rolling elements, there have been developed the slider, especially carriage with a variety of crowning profile.
In a commonly-owned Japanese Laid-Open Patent Application No. 2005-273,765, there is disclosed a linear motion guide unit in which a carriage was machined to crown the race profile. With the prior linear motion guide unit as stated earlier, the raceway surfaces grooved in the carriage for the load-carrying races are machined at their ingress/egress areas to crown the raceway surfaces to modify the load-carrying race profile into the crowning profile of gentle curvature, and further made at their forward and aft ends with rounded bevels, one to each end, each of which is made in a curved contour merging into the associated crowning profile without causing any discontinuity at a junction or boundary of the rounded bevel with the crowning profile. The crowning profile extends across a length as twice as the diameter of a rolling element. Moreover, the crowing profile is made on the carriage to have a depth set to an equivalent of an amount of elastic deformation that might occur in the raceway surface when the load-carrying race undergoes the load reaching a half of a static nominal standard load. The crowning profile is worked out simultaneously with the raceway surface on the carriage, so that the crowning profile is made to merge evenly into the associated raceway surface.
Another linear motion guide unit is disclosed in Japanese Laid-Open Patent application No. 2000-46,052, which is better resistant to any impact or shock, effective to contain any vibration caused owing to rolling movement of the rolling elements and to keep the rolling elements against wobbling motion during rolling traveling, and further made less in variation in frictional resistance. This prior liner motion guide unit is composed of a guide rail and a slider that fits over or conforms to the guide rail for movement relative to the guide rail, the slider being made up of a carriage, end caps and more than one rolling element. The carriage is made to have the overall length of 20 to 50 times as long as the diameter of the rolling element. The prior art is considered to be only the linear motion guide unit having the slider greater in length than ever known.
A further another linear motion guide unit is disclosed in Japanese Laid-Open Patent application No. 2004-138,193, in which an area to crown the race profile is defined to reduce any wobbling motion of the rolling elements, which would occur when they rolled through the load-carrying races. The linear motion guide unit is composed of a guide rail having raceway surfaces, a slider having raceway surfaces in opposition to the raceway surfaces on the guide rail and conforming to the guide rail for linear movement along the raceway surfaces on the guide rail, and more than one rolling element interposed between the opposite raceway surfaces on the guide rail and the slider to roll through there. The raceway surfaces inside the slider are made slope at particular areas near their lengthwise ends to provide crowning profiles there. The interrelations among the effective length of a crowning profile, Lce, the overall length of the crowning profile, Lc, the diameter of a rolling element, Da, and the length of a bevel, C, are referred to Lce/Da≧1 and also (Lc−C)/Da≦3. With the linear motion guide unit as stated just earlier, the crowning profile in length is needed to at least satisfy Lc/Da<3.
Besides being able to work with high accuracy, for example high accuracy of submicron (a ten-thousandth mm) level in traveling performance and position control, the linear motion guide units to be used in a variety of machines including machine tools, semiconductor fabricating equipments, measurement instruments, assembling machines, and so on are needed to have high rigidity or stiffness sustainable against heavier machinery or large-sized work.
With the linear motion guide units installed in the machinery as stated earlier, conventional practice is to crown the raceway surface in the carriage and modify the raceway profile as recited earlier to make sure of high accuracy and high stiffness of the load-carrying races in the carriage of the slider. In the linear motion guide unit disclosed in the commonly-owned Japanese Laid-Open Patent Application No. 2005-273,765 as recited above, the crowning made on the carriage extends across twice as long as the diameter of the rolling element. Nevertheless, the crowning length made as stated just above was later proved insufficient for the carriage that is made extremely large in length, called ultra-long type to make certain of the stiffness or rigidity.
With the prior linear motion guide unit as recited second, although the carriage in the slider is seemed made larger in length, it is unknown whether the construction renders the slider substantially viable. Moreover, the linear motion guide unit as recited third is of the type in which the balls are selected as rolling elements. The crowning profile extends at longest across about a matter of one to three times the diameter of the ball. Any further crowing is described to be refrained because of making the rigidity or stiffness less. The third prior art recited as stated earlier discloses no technical concept of the crowing length across four times or more the diameter of the rolling element and therefore is insufficient for the machinery that expects high stiffness as well as high accuracy of the linear motion guide units. Thus, it still remains a major challenge to develop the linear motion guide unit, which is high in both the accuracy and stiffness performances and further rich in durability or long-lasting service life when used in the machinery including machine tools, semiconductor fabricating equipment, measurement instruments, assembling machines, and so on.